This invention relates to an improved cargo container spreader or grappler spreader which includes radio-controlled apparatus for accomplishing the functions for which the spreader is designed. More particularly, this invention relates to switching means, including proximity switches on the four corners of the spreader, to control energization of the locking and unlocking circuits for the container-engaging twist locks. In addition, this invention relates to an improved expansion and retraction circuit and to a backup safety circuit for the locking and unlocking circuits of the spreader.
U.S. Pat. No. 3,858,728 discloses a crane and spreader combination for handling cargo containers which includes a spreader lacking the usual cable supply power facilities. A portable self-sufficient power unit with quick disconnect fittings mates with corresponding fittings of the spreader. The crane is equipped with a radio transmitter and the spreader with a radio receiver for controlling by radio the various features and functions of the spreader apparatus. That patent (hereinafter referred to as the '728 patent) is assigned to the assignee of this invention and is hereby incorporated by reference.
The '728 patent discloses a latch system for locking the spreader to a container, a plurality of corner guides movable into and out of an operable position relative to the container which guides in a lower operable position assure registry of a spreader with a container and a mechanism for expanding and contracting the length of the spreader and actuation of the grappler arms, among other features.
It is desirable to improve the operation of a spreader of the type described in the '728 patent by the inclusion of additional safety features to prevent the premature locking and accidental unlocking of the twist locks, particularly since the electrical and hydraulic circuits on the spreader are radio controlled from a transmitter located in the cab of a crane. A reason for such an aim is because the operator may be positioned where his view of the container is obstructed. In addition, it is desirable to provide a hydraulic safety circuit for sensing and controlling the pressure in the hydraulic locking and unlocking circuit to prevent accidental unlocking while the container is suspended. In addition, it is desirable to improve the expansion and retraction circuit, especially when the spreader is extended at or near its outermost position.
Accordingly, it is a principal object of this invention to provide an improved spreader arrangement and particularly a radio-controlled spreader, for handling containers which arrangement includes safety circuits for preventing the premature locking and accidental unlocking of the twist locks under various conditions.
It is another object of this invention to provide for a radio-controlled expandable spreader which has an improved expansion and retraction circuit.
It is another object of this invention to provide a switching circuit, including proximity switches on the four corners of the grappler spreader, to sense the presence of the container and thus to control the energization of the locking and unlocking circuits on the spreader in order to prevent premature locking and accidental unlocking.
It is another object of this invention to provide a backup safety circuit for the hydraulic locking and unlocking circuits to prevent an inadvertent unlocking of the twist lock in the event an operator accidentally selects an unlock position while a container is suspended by the spreader and the proximity switches are out of adjustment.
These and other objects, aims and advantages of the invention will become apparent from the following written description of the invention, taken in conjunction with the accompanying drawings.